In one of the preservation techniques for foods, and so on, an oxygen absorbent is used. In this method, a product to be preserved and an oxygen absorbent are both kept in a sealed gas barrier bag or a sealed container (hereinafter collectively referred to as “sealed container”). By allowing the oxygen in the sealed container to be absorbed in the oxygen absorbent and keeping the storage atmosphere in an oxygen free condition, the oxidative degradation of the quality of contents and the proliferation of bacteria or microorganism are prevented. This method has been extensively used for keeping the quality of products which are susceptible to oxidative degradation. In view of oxygen absorbing capability, ease of handling, safety, cost, and so on, oxygen absorbents containing an iron powder as the oxygen absorbing substance, i.e., as the main ingredient have been hitherto used. In the application requiring an inspection using a metal detector or an X-ray inspection system, an organic compound such as ascorbic acid and glycerol and so on is used as the main component instead of the iron powder.
The oxygen absorbent is required to be smaller in its size. The more small size reduces, the more a strange feel during the preservation of foods reduces and the more enables the application to a container with a limited space for the oxygen absorbent, to broaden the filed of application.
Since hitherto, oxygen absorbent pouches contained iron metal are usually produced directly from a powdery mixture, the volume of the pouch must be designed taking the spread of the powder upon filling into consideration. An oxygen absorbent needs water or moisture to exhibit its oxygen absorbing performance. Therefore, a water or moisture supplying component is required to add to the oxygen absorbing component to absorb oxygen even in an atmosphere having a relatively small water or low moisture content, thereby requiring a larger volume.
In these circumstances, it has been attempted to reduce the size by increasing the activity of the main ingredient so as to reduce the filling amount. For example, Patent Document 1 proposes to coat the main component iron powder with a metal halide. However, the increasing of activity have limited extent. Therefore, it is still demanded to develop other techniques.
In view of merely enhancing the activity, it is known that the oxygen absorbing speed and the oxygen absorbing rate can be improved by selecting an oxygen absorbing promoter. However, there is a problem that a well flowable mixture is not obtained, to make the filling package into pouches impossible.
In the above circumstances, it has been proposed to make a powdery mixture (oxygen absorbent composition) into a molded body, thereby preventing the scattering of powder to reduce the volume. On the basis of this proposal, there has been developed a tablet type oxygen absorbent which is independent of the atmospheric humidity.
However, the molding requires necessarily to reduce the volume by pressure. This reduces significantly the reactive surface area to make the oxygen absorbing speed extremely low. Therefore, the proposed technique cannot be used in the application which indispensably requires an ordinary oxygen absorbing speed, for example, a speed which reduces the oxygen concentration of atmosphere to less than 0.1% within about two days.
Moreover hitherto oxygen absorbents for the application which needs a foreign matter inspection using a metal detector or an X-ray inspection system have been produced by impregnating a carrier with a solution of an easily oxidizable main component organic substance composed of ascorbic acid and glycerol and so on.
Since the oxygen absorbing capacity per unit volume increases as the supported amount of the solution of easily oxidizable organic substance on the carrier is increased, a carrier capable of supporting a larger amount is used. As such carrier, a natural inorganic carrier has been hitherto used. Recently, the oxygen absorbing capacity is successfully improved by the use of a chemically synthesized carrier.
In the method of impregnating the carrier with the solution of the easily oxidizable organic substance, the supported amount of the solution is substantially constant if the kind of carrier is the same. Therefore, the content, i.e., the dissolved amount of the easily oxidizable organic substance in the solution is required to be larger for enhancing the oxygen absorbing capacity per unit volume. However, the oxygen absorbing speed is unfavorably reduced if a solution with a high concentration of the easily oxidizable organic substance is supported in a large amount. This may be due to the reduction in the reactive surface area necessary for the oxidation reaction.
Patent Document 1: JP 54-35883A